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(No Model.)

E. THOMSON. METHOD OE AND MEANS FOR PREVENTING MAGNETIC LEAKAGE.

No, 534,731. Patented feb. 26, 1895.

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ELIHU THOMSON, OF SWAMPSCOTT, ASSIGNOR TO THE GENERAL ELECTRIC COMPANY, OF BOSTON, MASSACHUSETTS.

METHOD OF AND.MEANS FOR PREVENTING MAGNETIC LEAKAGE.

SPECFICATION formingpart of Letters Patent No. 534,731, dated February 26, 1895.

Application filed February 6, 1893- Serial No. 461.155. (No model.)

To @ZZ whom t may concern,-

Be it known that L ELIHU THOMSON, a citizen of the United States, residing` at Swampscott, county of Essex, and State of Massachusetts, have invented certain new and useful Improvements in Methods of and Means for Preventing Magnetic Leakage, of which the following is a specification.

My invention relates to apparatus in which electric currents are generated by induction, such as alternating current dynamos, transformers, and the like. The principle of these machines is now well understood, the induced current being excited by the lines of force or magnetic field developed in the vicinity of the primary coil. The currents induced, bowever, set up a counteracting field of force which reacts upon the field of the primary Vand detlects its lines of force so as to cause magnetic leakage between the two coils. This effect becomes more and more pronounced as the current increases, until finally the current in the secondary reaches a certain maximum strength, which is unalterable by any increase in the current fiowing in the primary coil.

My invention has for its object therefore, to prevent this magnetic leakage and to compel the lines of force of the primary field to cut the secondary coil under any changes in the strength of the primary current. It is applicable to all apparatus using alternating current. I have however described it herein applied to a transformer as a convenient embodiment of my invention.

The invention is based on the general principle that if a magnetic field be so produced that the lines tend in a given direction from the inducing coil, then a closed circuit conductor so supported as to surround these lines as they pass through its axis, will react upon them, producing an opposing iield and keeping out the major part of the lines by the induction of a strong current in the conductor, which opposes vthe propagation of the magnetic field through its axis. The closed conductor may be said to be opaque to the field, or, as it is often expressed, it beats it back.

My invention therefore consists, in one speciiic aspect, in arranging adjacent to the primary and secondary coils an accessory closed circuit, preferably of low resistance, so located as not to be intersected bythe lines of the primary field when this occupies its normal position, but to be cut by those lines when forced out of place by the counter Iield of the secondary. The accessory circuit must be capable of developing a stronger field than the secondary, to attain the best effect, so that, by its opposition, it may drive back the 6o deflected lines of force, thus preventing magnetic leakage, and permitting the primary to induce in the secondary a current proportional to the strength of the primary current,

up to the limit for which the apparatus is designed.

in the construction of transformers, it is impossible to so closely associate the primary and secondary coils as to make them occupy virtually the same space, which is essential 7o to the complete response of the primary current to any increased load on the secondary.

If this could be done, every change of the secondary current would give rise to a corresponding and equivalent change in tne primary, and there would be no leakage of magnetism, and no difficulty arising from self-induction of the secondary coil and therefore no means would be required to compensate for or remove the leakage iield.

The use of my invention forms a convenient means of accomplishing the same result as if the coils could be arranged in the way pointed out.

The accompanying drawings show embodi- S5 ments of my invention, wherein- Figure l is a section upon the line l-l of Fig. 2. Fig. 2 is a plan. and i are Figs. o diagrams showing sections of transformers with and without my invention. Figs. 5 and 9o 6 illustrate the application of my invention to an alternating current dynamo. Figs. 7 and 8 show a side elevation and plan respectively of the application of my invention to an induction coil.

In the ligures, the coreA is shown as wound with the primary coil B and the secondary coil C concentric therewith. There is necessarily a space between the coils and a consequent leakage of the lines of force, as indiron cated in Figs. 3, 5, and 7. The accessory coils D consist of endless strips of copper or other good conductor, placed adjacent to the primary and secondary coils, so as to intersect the leaking lines of force, as already pointed out. They are not parallel to the coils, but form a circuit returning upon itself and of greater inductive capacity than the secondary, as already pointed out in the statement of invention.

As shown in Figs. 5 and 6, the accessory coil D is applied to an alternating current dynamo by placing it between the adjacent coils E, E on the core F of the field-magnet, in a position to intercept the lines 0c which leak out between the coils E, E.

As applied to the induction coil, the endless strips D2 are slipped between the iron core B and its Winding C, as shown in Figs. 7 and S. If alternating or periodic currents are passed through the coil C', this arrangement prevents the magnetic lines from lateral diversion in the direction of the arrow, and they are, for the most part, Aforced by the presence of the conductor D2 out through its end, and their action upon a core, a conductor or other responsive object, is increased for some distance from the core B.

In all of the illustrations, it will be noted that the shield is a closed circuit parallel to neither the primary nor secondary coils, but is a circuit which returns on itself, and whatever current is induced in it by the primary, in returning, goes in the opposite direction around the axis and thereby assists the secondary by the inducingr current near this secondary flowing in the same direction as in the primary. For example, the primary current induces in that portion of the shield near it a current in the opposite direction to itself. This current, however, by the arrangement of the closed shield, reverses its direction, pass' ing near the secondary in the same direction as the primary current, and therefore has the same effect upon the secondary as though the primary coil had been brought over and superimposed upon it. The action of this closed conductor is very much as though the magnetic medium Within its axis had been removed or a strong diamagnetic substance had been placed there instead. It may be considered to be in effect, for an alternating field, very much like a diamagnetic shield for continuous currents, assuming` that there is a diamagnetic material of such quality as to have astrong effect in stopping magnetic lines of force.

Vhat I claim as new, and desire to secure by Letters Patent, is-

l. The method of preventing magnetic leakage between adjacent magnetic poles, which consists in setting up an accessory field adapted to oppose such leakage.

2. The method of preventing magnetic leakage between adjacent magnetic poles, which consists in causing such leakage to create an accessory opposing field.

3. The method of preventing magnetic leakage between the coils of an alternating electric current apparatus, which consists in set ting up an accessory field adapted to oppose the leaking lines of force, substantially as described.

4. The method of preventing magnetic leakage between the coils ot an alternating electric current apparatus, which consists in causing the leaking lines of force to create an accessory opposing field, substantially as set forth.

5. The method of preventing magnetic leakage between the coils ot an alternating electric current apparatus, which consists in causing the leaking lines of force to set up an accessory opposing field in an adjacent coil, substantially as described.

G. A device for preventing magnetic leakage between the coils of an alternating current electric apparatus, consisting of an accessory coil placed adjacent to but normally out ot the primary field, substantially as set forth.

'7. A device for preventing magnetic leakage between the coils of an alternating electric current apparatus, consisting of an endless conductor placed out of the normal primary tield,but adapted to be cut by the lines of force when deflected from their normal position, substantially as described.

In testimony whereof I have hereunto set my hand this 2d day of February, 1893.

ELIHU THOMSON.

Viiitnesses:

JOHN W. GIBBONEY, BENJAMIN B. HULL. 

